(1) Field of the Invention
The invention relates to an electronic intermitter, and, more particularly, to a system for controlling the cyclic, intermittent operation of a device.
(2) History of the Prior Art
There are numerous applications for a system for controlling the intermittent operation of a device, or of another system, which operation requires a high degree of precision in that control. For example, in the "burn in" of certain electronic devices and components, it is desirable to operate the devices for a selected period of time under chosen load and environmental conditions and turn the devices off for another select period of time. By cycling the device through numerous successive "on" and "off" conditions, actual device performance in the field can be simulated to experimentally ascertain the life of the device or its behavior under operating conditions.
Another environment in which intermitter controllers are especially useful is in the control of the flowing gas wells. To produce a flowing gas well in certain geologic formations, it is necessary to employ the practice of periodically "shutting-in" the well. The well is closed off to allow sufficient pressure to build up within the well over a carefully pre-selected period of time so that when the well is subsequently opened up, all the fluids which have built up within the well will be expelled through the sales line system. That is, production of the well occurs only periodically during a relatively short period of time, for example, 15 minutes, while the well remains "shut-in" for a substantially greater period of time, for example, 4 hours. The respective shut-in time and production time which are optimum to produce maximum gas from a given flowing well are unique to each well and each case is determined experimentally. These times are also quite critical. Failure to shut-in a well within even a few minutes of the proper time envelope for that particular well could result in complete loading of the well which may require it to be shut-in for an extended period of time, for example, 48 hours, in order to obtain production again.
Intermittently operated flowing gas wells may sometimes exhibit erratic output pressure characteristics. That is, a well just cycled to the "on" condition characteristically begins to drop in pressure as gas is delivered and continues to drop until "off" cycle begins. Sometimes the pressure may begin to drop and suddenly, due to the flow characteristic of the well, the pressure will rise again for a short time before again beginning its decent. In these instances it would be desirable to place the operation of "on" timing on "pause" 9nd suspend counting during the time period of the burst of increased pressure and extend the production time by an amount equal to the extra gas which happens to be available at that moment. Similarly, if the rising pressure during an "off" cycle takes a sudden dip for a time before it begins its rise toward production pressure again, it is desirable to "pause" in the "off" cycle timing to compensate for the erratic pressure drop.
A prior art system which performs many of the essential functions for intermitting a gas well is shown in U.S. Pat. No. 4,150,721 issued to Norwood. The Norwood system includes a digital read-out and a series of manually actuated thumb wheel switches for selecting the desired "on" and "off" times for intermitting a well. While an improvement over prior art mechanical intermitters the Norwood system still embodies numerous disadvantageous features. For example, the Norwood system requires the on-site presence of an operator to physically reset the mechanical switches to change cycle times rather than being remotely operable as in the system of the present invention. The present system also includes a true programmable memory which may be addressed by small membrane type switches easily mounted in a panel so as to provide a sealed gas tight enclosure. The memory also allows full flexibility in the range of times which may be programmed, i.e., hours/minutes or minutes/seconds.
The intermitter controller of the present invention includes a motor valve failure alarm system wherein the failure of pressure in the output of the controller to said motor valve after a pre-selected period of time results in an alarm condition shutting down the entire controller. The system also has provision for a plurality of external signals which bear upon and indirectly control the desired operational state of the controller. To allow for maximum flexibility in the on and off times of intermitter operation, the system of the invention includes means for changing the timing range to accommodate programmed time in either hours/minutes or in minutes/seconds.